By PAUL L. SCHNIRRING

The 1980 census confirmed Illinois' slower growth rate which, in the short term at least, is bad news. Illinois was already braced for the loss of two congressional seats and of some federal funds. But there have also been significant population shifts within the state, including a surprising population decline in the older suburbs that surround the City of Chicago.

ILLINOIS WILL LOSE as a result of the 1980 census. Population in Illinois grew at a much slower pace than did that of the nation as a whole over the last 10 years, with the result that Illinois will lose two seats in Congress and some federal funds. Illinois' 1980 population is 11,418,461, or 5 percent of the total U.S. population. This is a decrease of .5 percent since 1970 as a percentage of the nation's population.

The immediate effect of the decrease in Illinois' share of the U.S. population is the loss of the two Congressional seats, bringing Illinois' total down to 22 seats in the U.S. House. The long-range effect, in terms of federal funding, is more difficult to assess.

Illinois' growth (as well as the nation's) from 1970 to 1980 is more apparent than real. This is due mainly to the undercount in the 1970 census and the apparent lack of an undercount in the 1980 census. It is commonly accepted that the undercount in 1970 was about 2.5 percent nationwide. For the 1980 census, the Bureau of the Census estimates that the undercount is very near zero (about .5 percent or less), illegal aliens excluded. Final population counts were 4.5 million higher than anticipated.

Although Illinois' population statewide showed only slow growth (see table 1), there were considerable shifts within the state. The northern half of the state revealed a relatively stable population with two exceptions; shifts within Chicago and its close suburbs, and a population decline in a string of counties stretching from Vermilion County north-westerly to Carroll County. Most of Southern Illinois posted population increases, except for the Illinois portion of the St. Louis metropolitan area.

Analyzing population county by county from 1970 to 1980, significant changes become evident; DuPage County gained the most people, 170,211; Kendall County grew at the fastest rate, 41.1 percent; Cook County lost almost a quarter of a million people (from 5,493,766 in 1970 to 5,253,190 in 1980); St. Clair County (East St. Louis) lost the largest percentage (-7.0 percent), changing from 285,591 to 265,469.

The "collar counties" around Chicago were the only group of counties where growth was concentrated. While Illinois as a whole gained 308,176 from 1970 to 1980, these five collar counties alone gained 368,149.

Illinois remains a largely metropolitan state, with 81.0 percent of its residents living in metropolitan areas. This is a decrease of only .5 percent from 1970. The 1980 census shows over 9 million of the state's inhabitants reside in one of Illinois' 10 standard metropolitan statistical areas (SMSA's) (see table 2).

Although Cook County as a whole lost 240,576 people, the Chicago SMSA (Cook, DuPage, Kane, Lake, McHenry and Will counties) gained the most people, 127,573. Yet the Chicago SMSA's gain as a percentage increase tied for the eighth lowest rank of the 10. The Bloomington-Normal SMSA grew the fastest (14.1 percent), while only the St. Louis SMSA (Illinois portion) declined (3.0 percent).

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The 1980 census has changed the aggregate size of Illinois' SMSA's, and it shows significant shifts in population within individual SMSA's. Specifically, from 1970 to 1980, the population of the City of Chicago declined from 3.37 million to just above 3 million; the County of DuPage grew from 487,966 to 658,177, yet the total population of the entire Chicago SMSA increased 1.8 percent.

It was no surprise that the City of Chicago, like other central cities, declined in population. However, the 1980 census reveals a new, more dramatic trend. An entire band of old suburbs circling the central city declined in population. This band of decline stretches from eastern Lake County through western Cook County into DuPage County and south to Will County (see Chicago area map). Most of these suburbs gained in population from 1960-1970, so the 1980 decline was striking.

Population is rising and falling in Illinois cities, and the extreme rates are mainly in the Chicago SMSA. Of the 64 cities with a population of 25,000 or more, the 10 fastest growing are all in the Chicago SMSA (see table 3); eight of the 10 with the highest rates of decline are also in the Chicago SMSA. The other two are East St. Louis and nearby Alton. Of the 118 smaller cities, ranging from 10,000 — 24,000 population, the 10 fastest growing have more than doubled their populations between 1970 and 1980. Nine of these 10 are in the Chicago SMSA; the other is Bourbonnais in Kankakee County.

One question still to be answered is how the 1980 census will affect the flow of federal funds to Illinois.

Approximately $50 billion in federal formula programs are allocated to the states. As a result of the decline in Illinois' relative share of the U.S. population, it may lose funds for programs based on population. The office of planning with the Illinois Bureau of the Budget has been examining over 100 federal programs allocated by formulas which include population as a factor. The question is how much impact the 1980 census will have on Illinois' share of these funds. Three factors may help cushion the impact on the state.

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First, many federal programs funded by formulas based on population use population estimates which are updated each year by the census bureau. In such cases, Illinois' share of the national allocation has been gradually revised throughout the 1970's and will not change significantly because of the 1980 census.

Second, many of the formulas are based on detailed census variables not available until 1983, which means there will be no effect until fiscal 1984. Some examples of federal programs based on these more complicated formulas are Medicaid, Community Development Block Grants and Aid for Elementary and Secondary Education.

In addition, many of the formulas have nondemographic components, some weakly or even negatively correlated with population change. Other formulas have "hold-harmless" provisions which prevent funding levels from dropping if population declines. Another stabilizing factor in formula funding is the limits imposed for the minimum and maximum amounts any state can receive.

The third factor, of course, is that the formulas themselves are not sacrosanct nor are the programs. The Reagan administration may make significant changes, particularly if formula-based programs are rolled into block grants. □

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